1. Field of the invention
The present invention relates to a magnetic recording medium comprising a nonmagnetic support and a magnetic recording layer, and a process for the preparation of the same. More particularly, the invention relates to a magnetic recording medium having a magnetic recording layer which shows a low friction coefficient and showing superior running property.
2. Description of prior art
A magnetic recording medium comprising a nonmagnetic support and a magnetic recording layer provided thereon is used as an audio tape, a video tape, or a recording medium for a computer system. The magnetic recording layer comprises a binder and a ferromagnetic powder dispersed therein.
A magnetic recording medium is desired to have a magnetic recording layer showing a low friction coefficient, because the magnetic recording layer records signals and reproduces the recorded signals while the surface of the magnetic recording layer is kept in contact with a magnetic head.
Recently, demand for a recording system of enhanced density has increased, and hence a more minimized ferromagnetic powder has been employed. The employment of such minimized ferromagnetic powder makes the surface of the magnetic recording layer very smooth, so that the friction coefficient on the surface of the magnetic recording layer tends to increase.
For reducing the friction coefficient on the surface of the magnetic recording layer, a lubricant such as fatty acid, a fatty acid ester, silicone oil or paraffinic hydrocarbon is generally incorporated into the magnetic recording layer. However, in the method of incorporating the lubricant into the magnetic recording layer, a large amount of such lubricant has to be employed because the lubricant is uniformly distributed in the whole magnetic recording layer including its bottom portion.
In such magnetic recording layer, the lubricant existing on the surface of the magnetic recording layer simply deposits on the recording layer, and hence the lubricant is liable to adhere to a supporting rod or a magnetic head equipped in a recording and reproducing device and drop off from the recording layer when the recording layer is repeatedly run in contact with the supporting rod or the magnetic head. Accordingly, the lubricant on the recording layer is easily removed in the running procedure.
Further, since a large amount of lubricant is used, the lubricant sometimes serves as a plasticizer for the binder to lower the mechanical strength of the magnetic recording layer.
The above-mentioned conventional magnetic recording medium is not improved sufficiently in the running property, although the electromagnetic conversion characteristics required for high density recording are improved.